Scattering display for contrast enhancement including target

ABSTRACT

A display comprising optical means for presenting an absence of light over a controlled viewing angle and means for selectively scattering or transmitting light in response to a prescribed input to effect a display of information within said viewing angle.

This is a continuation of application Ser. No. 645,457 filed Aug. 18,1984 and now abandoned.

The present invention relates generally to displays, and moreparticularly to displays including an optical system for enhancing adisplay of information.

Visual display devices may utilize liquid crystals. The property ofliquid crystals that enables them to be used in visual displays is theability of liquid crystals to transmit light in a strictly aligned orfield-on state, and to scatter light and/or to absorb it (especiallywhen combined with an appropriate dye) in a relatively free or field-offstate. An electric field may be selectively applied across the liquidcrystals to switch between field-off and field-on states.

Frequently a visual display device using liquid crystals displays darkcharacters on a gray or relatively light background. In such devices, itis desirable to improve the effective contrast between the charactersdisplayed and the background, and to reduce or eliminate front surfaceglare from the display.

There are three categories of liquid crystal materials, namely,cholesteric, nematic and smectic. The present invention relates in apreferred embodiment described hereinafter to the use of nematic liquidcrystal which is operationally nematic. By "operationally nematic" ismeant that, in the absence of external fields, structural distortion ofthe liquid crystal is dominated by the orientation of the liquid crystalat its boundaries rather than by bulk effects, such as very strongtwists (as in cholesteric material) or layering (as in smecticmaterial). Thus, for example, a liquid crystal material including chiralingredients which induce a tendency to twist but which cannot overcomethe effects of the boundary alignment of the liquid crystal materialwould be considered to be operationally nematic. A more detailedexplanation of operationally nematic liquid crystal material is providedin co-pending U.S. patent application Ser. No. 477,242, filed Mar. 21,1983 in the name of Fergason, entitled ENCAPSULATED LIQUID CRYSTAL ANDMETHOD, assigned to Manchester R&D Partnership, the disclosure of whichis hereby incorporated by reference. Reference may also be made to U.S.Pat. No. 4,435,047, issued Mar. 6, 1984, in the name of Fergason,entitled ENCAPSULATED LIQUID CRYSTAL AND METHOD, assigned to ManchesterR&D Partnership, which disclosure is also hereby incorporated byreference.

The operationally nematic liquid crystal is contained in a containmentmedium that forms volumes of liquid crystal material. The liquid crystalmay be contained in discrete capsules or in a containment medium thattends to form a multitude of capsule-like environments wherein thecapsules may be interconnected by channels containing liquid crystalmaterial. In the field-off condition, or any other condition whichresults in the liquid crystal being in a distorted or randomly alignedstate, the liquid crystal structure is distorted to a curved form (hencecurvilinearly aligned) wherein the spatial average orientation of theliquid crystal over a capsule-like volume, for instance, is stronglycurved and there is no substantial parallel directional orientation ofthe liquid crystal in the absence of a prescribed input.

Preferably, the operationally nematic liquid crystal has a positivedielectric anisotropy, and has an ordinary index of refraction thatsubstantially matches that of the containment medium. Such material willcause scattering of light incident thereon in the field-off orrelatively free state. This liquid crystal material, described in detailin the above-identified U.S. Pat. No. 4,435,047, may be designatedencapsulated operationally nematic liquid crystal material or nematiccurvilinearly aligned phases ("NCAP") liquid crystal material.

The present invention, however, is not limited in use to NCAP configuredliquid crystal. Certain embodiments of the invention may be employedwith any of the various types of liquid crystal materials orconfigurations thereof that selectively scatter and/or absorb ortransmit light in response to a prescribed input.

Usually liquid crystal is anisotropic both optically and, for example inthe case of nematic liquid crystal, electrically. The optical anisotropyis manifest by the scattering of light when the liquid crystal is inrandom alignment, and the transmission of light through the liquidcrystal when it is in ordered alignment. The electrical anisotropy maybe a relationship between the dielectric constant or dielectriccoefficient with respect to the alignment of the liquid crystalmaterial.

The present invention relates to improvements in displays as well as tothe utilization of the light scattering characteristic of liquid crystalmaterials in displays. The invention also relates to the use of suchmaterials and characteristics, for example, to obtain relatively darkcharacters or information displayed on a relatively bright background inboth small and large size displays. Additionally, an embodiment of thepresent invention provides a display in which front surface glare is allbut eliminated.

An object of the present invention is to provide a display having arelatively high quality of optical brightness and contrast.

Another object of the present invention is to provide a displayincluding an optical system for enhancing the display of information,the information displayed being vividly contrasted to its background.

A further object of the present invention is to provide a liquid crystaldisplay wherein focused light and scattered light are utilized to createa dark character on a very bright background.

A still further object of the present invention is to provide a displaywherein front surface glare is all but eliminated.

As may be seen hereinafter, the display disclosed herein is one whichmay include an optical means for presenting an absence of light over aviewing angle and means for selectively scattering or transmitting lightin response to a prescribed input to effect a display of informationwithin the viewing angle.

A liquid crystal means may be utilized for selectively scattering ortransmitting light in response to a prescribed input. The optical meansmay present an absence of light over the viewing angle by focusing lighttransmitted by the liquid crystal means onto a target means. The liquidcrystal means may comprise NCAP liquid crystal. Materials other thanliquid crystal, such as electrophoretic materials, which scatter lighton one hand and transmit it on the other, however, may also be utilizedin the context of the present invention.

The target means may comprise a black absorber for absorbing at leastsubstantially all of the light incident thereon. The optical means maycomprise a reflecting concave means for focusing light transmitted bythe liquid crystal means within a controlled viewing angle onto a targetmeans disposed between the liquid crystal means and the reflectingmeans.

In another embodiment, the optical means may comprise a lens meansdisposed between the liquid crystal means and the target means forfocusing light from an observer within a prescribed viewing angle ontothe target means. This embodiment also is preferably illuminated fromthe rear.

In yet another embodiment, the optical means may comprise a concavereflector means located on a non-viewing side of the liquid crystalmeans to focus light onto a light absorbing target means located on aviewing side of the liquid crystal means. The reflector means and theliquid crystal means present a concave surface to light incidentthereon. This embodiment not only enhances contrast but eliminates frontsurface glare.

The concept of this embodiment provides a method and apparatus forreducing glare from a display by focusing specular reflection from aconcave reflecting surface onto a light absorbing target means. Thisembodiment is not limited to use with materials that transmit or scatterlight in response to a prescribed input. The concave configuration ofthis embodiment provides for glare reduction in both electro-optical andnon-electro-optical devices. For example, the concept of this embodimentmay be utilized to reduce glare from a white-faced chalkboard or aglossy-faced sign.

The prescribed input is preferably of the electromagnetic type and, moreparticularly, an electric field. The apparatus may include electrodesfor applying the electric field. The electrodes may be located onopposite sides of the liquid crystal means. Substantially opticallytransparent substrate means may support the electrode means, and acircuit means may be provided to selectively energize the electrodemeans to apply the electric field.

In accordance with one aspect of the present invention, a liquid crystaldisplay, such as a billboard, can produce relatively dark characters,information, etc. on a relatively dark characters, information, etc. ona relatively bright or white background. The bright background may beproduced by liquid crystal material that is randomly aligned in thefield-off state wherein light incident on the liquid crystal material isscattered. The dark character is caused, for example, by liquid crystalmaterial that is in a field-on state or in ordered alignment and, thus,substantially optically transparent such that incident light isappropriately focused onto the target means. When the liquid crystalmaterial is randomly aligned, only the relatively bright backgroundappears. When a selected portion of the liquid crystal material isorderly aligned, a very dark character may appear against the verybright background to an observer within the viewing cone or viewingangle of the display. The foregoing may be accomplished using relativelylow power requirements and minimum liquid crystal material.

The display of the present invention will be described in more detailhereinafter in conjunction with the drawings wherein:

FIGS. 1 and 2 are schematic views that illustrate a liquid crystalapparatus in the field-off and field-on states, respectively, that maybe utilized in the present invention;

FIG. 3 is a schematic, side elevational view illustrating one embodimentof the display of the present invention;

FIG. 4 is a schematic ray trace illustrating the operation of theembodiment of FIG. 3;

FIG. 5A is a schematic, side elevational view illustrating anotherembodiment of the display of the present invention;

FIG. 5B is a perspective view illustrating a further embodiment of thedisplay of the present invention;

FIG. 6 is a schematic ray trace illustrating the operation of theembodiment of FIG. 5B;

FIG. 7 is a schematic, side elevational view illustrating yet anotherembodiment of the display of the present invention;

FIG. 8 is a front elevational view of the embodiment of FIG. 7; and

FIG. 9 is schematic ray trace illustrating the operation of theembodiment of FIGS. 7 and 8.

Referring now to the drawings, attention is first directed to FIGS. 1and 2. FIGS. 1 and 2 show a liquid crystal apparatus indicated generallyby reference numeral 10. The apparatus includes a layer or layers ofliquid crystal 11 supported on a substrate 12 having an electrode 13located thereon. The apparatus may further include a second electrode 14mounted on a substrate 18.

The liquid crystal may comprise any liquid crystal material orconfiguration of liquid crystal material which selectively scatters ortransmits light in response to a prescribed input. For example, theliquid crystal may by configured as a twisted nematic apparatus. In apreferred embodiment, the liquid crystal is configured in a curvilinearmanner (NCAP). A primary feature of the present invention is that theliquid crystal material will scatter light impinging thereon when in afield-off or random alignment state, and in the field-on or orderlyaligned state the liquid crystal material will be substantiallyoptically transparent.

Additionally, materials other than liquid crystal which scatter light onone hand and transmit it on the other in response to a prescribed inputmay be utilized in the context of the present invention. For instance,an electrophoretic material may be used.

The use of NCAP configured liquid crystal permits substrates 12 and 18to be flexible. This allows, as will be discussed in more detail below,the construction of a display in which front surface glare is all buteliminated. Particularly, the NCAP configured liquid crystal materialdisposed between the flexible electrode-coated substrates provide aflexible film that may be utilized to form a curved front surface of adisplay.

A voltage may be applied to electrodes 13 and 14, and hence acrossliquid crystal 11 from a conventional voltage source 16. Voltage source16 may be connected to the electrodes by electrical leads through aswitch 17. When the switch 17 is closed, the electrodes are energizedand apparatus 10 is in a field-on state with the molecules of the liquidcrystal material in the desired alignment to permit the transmission oflight. When the switch is open, the electrodes are de-energized andapparatus 10 is in a field-off state such that the liquid crystalscatters light.

The NCAP configured liquid crystal material, which is schematicallyillustrated in FIGS. 1 and 2, may include a liquid crystal material 20more or less contained within the confines or the interior volume 21 ofa capsule 22 or an encapsulating medium. The NCAP configured liquidcrystal material comprises a plurality of such capsules or anencapsulating medium in which liquid crystal material is dispersed.

Each capsule may be discrete or alternatively the liquid crystalmaterial 20 may be contained in a containment medium 23, such as a latexmedium as will be hereinafter discussed, that tends to form a multitudeof capsule-like environments containing the liquid crystal material. Inthis regard, the liquid crystal material 20 may be more or less confinedto an approximately spherical or otherwise curvilinear surface of acontainment cavity. Such cavities, however, may be interconnected, forexample, by one or more channels or passages. The liquid crystalmaterial would preferably be in both the discrete volumes or cavitiesand in the interconnecting passages. Thus, the internal volumes ofrespective capsules may be fluidly coupled via one or moreinterconnecting passages. All of the aspects and features of the presentinvention vis-a-vis individual unconnected capsules have been found tobe applicable to an arrangement of capsules that have one or moreinterconnecting passages.

Preferably, liquid crystal material 20 is nematic liquid crystalmaterial having positive dielectric anisotropy. Nematic liquid crystalmaterial has fluid-like properties that facilitate the conformance orthe distortion thereof to the shape of the capsule wall in the absenceof an electric field. On the other hand, in the presence of an electricfield such nematic material will relatively easily change to orderedalignment with respect to such field.

Liquid crystal material of a type other than nematic or combinations ofvarious types of liquid crystal material and/or other additives may beused with or substituted for the nematic liquid crystal material as longas it is operationally nematic in the containment medium. However,cholesteric and smectic liquid crystal material generally are bulkdriven. It is more difficult to break up the bulk structure thereof forconformance to capsule wall shape and energy considerations in thecapsule.

As shown in FIG. 1, in the field-off state, the molecules of liquidcrystal, depicted as dashed lines, conform to the shape of the cavitycontaining the liquid crystal. The directional orientation of a layer ofliquid crystal molecules may be distorted to curve in the direction thatis parallel to a proximate area of the wall surface 25 of a cavity. Moregenerally, all that is required is that the interaction between thecavity wall 25 and the liquid crystal material 20 produces anorientation in the liquid crystal near that wall that is generallyuniform and piecewise continuous, so that the spatial averageorientation of the liquid crystal material over the capsule volume isstrongly curved and there is no substantial parallel direction oforientation of the liquid crystal structure. It is this strongly curvedorientation that results in the scattering and polarizationinsensitivity (the liquid crystal material is insensitive to thedirection of optical polarization of incident light) in the field-offcondition.

In the field-on condition (See FIG. 2), or any other condition whichresults in the liquid crystal being in ordered or parallel alignment,the liquid crystal material 20 will transmit substantially all the lightincident thereon and will tend not to be visible. The light that istransmitted is that which is focused onto a target means to opticallyenhance a display, as discussed below. On the other hand, as noted, inthe field-off condition when the liquid crystal is in distorted orrandom alignment, some of the incident light will be absorbed, but mostof the incident light will be scattered.

The index of refraction of containment medium 23 and the ordinary indexof refraction (the index when an electric field is applied) of theliquid crystal material 20 should be matched as much as possible when inthe field-on state to avoid scattering. However, when the liquid crystalmaterial is in the field-off state, there will be a difference in theindices of refraction at the boundary of the liquid crystal material 20and the wall of capsule 22, for example. Specifically, the extraordinaryindex of refraction (the index with no electric field) of the liquidcrystal is greater than the index of refraction of medium 23. Thiscauses refraction at that interface or boundary and, thus, scattering.

As long as the ordinary index of refraction of the liquid crystalmaterial is closer to the index of refraction of the containment medium,than is the extraordinary index of refraction, a chance in scatteringwill result when going from field-on to field-off states, andvice-versa. For any given index of refraction, maximum contrast resultswhen the ordinary index of refraction of the liquid crystal matches theindex of refraction of the medium. The closeness of the index matchingwill be dependent on the desired degree of contrast and transparency inthe device, but the ordinary index of refraction of the liquid crystaland the index of the containment medium will preferably differ by nomore than 0.03, more preferably, 0.01, especially 0.001.

Preferably, the electric field E (See FIG. 2) is applied to the liquidcrystal material 20 for the most part rather than being dissipated ordropped substantially in the containment medium. There should not be asubstantial voltage drop across or through the material of which thecontainment medium is formed. Rather, the voltage drop should occuracross the liquid crystal material 20 within the volume 21 of thecapsule 22.

Additionally, the electrical impedance of the containment mediumpreferably should in effect be large enough relative to that of theliquid crystal such that a short circuit will not occur exclusivelythrough the medium to bypass the liquid crystal.

The dielectric constant of the material of which the containment mediumis formed and the dielectric coefficient of the liquid crystal, and theeffective capacitance values of the containment medium, particularly ina radial direction, and of the liquid crystal material across which theelectric field E is imposed, all should be so related that thecontainment medium does not substantially drop the magnitude of theapplied electric field E. Ideally the capacitance dielectric constants(coefficients) of the entire layer of NCAP liquid crystal should besubstantially the same of the field-on condition.

The liquid crystal material 20 will have a dielectric coefficient valuethat is anisotropic. It is preferable that the dielectric constant ofthe containment medium be greater than the dielectric coefficient of theliquid crystal material 20. The differential between the dielectriccoefficient for the liquid crystal material 20 when no electric field isapplied, which should be rather small, and the dielectric coefficientfor the liquid crystal material when it is aligned upon the applicationof the electric field, which should be relatively large, should be aslarge as possible. The critical relationship of dielectric values andapplied electric field should be such that the field applied across theliquid crystal material in the containment medium is adequate to causealignment of the liquid crystal with respect to the field. Therelationship between the dielectric constant of the containment mediumand the dielectric coefficient of the liquid crystal 20 may be achievedwhen the liquid crystal has a positive dielectric anisotropy.

In accordance with the present invention, substrates 12 and 18, andelectrodes 13 and 14 are optically transmissive so that liquid crystalapparatus 10 can control the transmission of light therethrough inresponse to the application of an electric field. Electrode 13 may, forexample, form a single common electrode surface while electrode 14comprises a patterned electrode having multiple electrode portions thatcan be selectively energized to apply the electric field to selectedportions of the liquid crystal material. For instance, as is well knownin the art, electrode 14 may be divided into seven electrically isolatedsegments, each of which may be selectively energized to display variousnumerical characters. Electrode 14 could also be configured to form adot matrix display comprising a plurality of dots or pixels arranged incolumn and rows. A row is enabled to accept display information inparallel via the column lines.

Preferably, a plurality of NCAP liquid crystals are applied to substrate18 in a manner such that the NCAP liquid crystals adhere to electrode 14and substrate 18. The material of which capsule 22 is formed is suitablefor binding or otherwise adhering the capsule to the electrode and/orsubstrate. In one embodiment, capsule 22 is formed of a polyvinylalcohol (PVA). In a preferred embodiment, the liquid crystal material isdispersed or entrapped in a latex containment medium. In eitherembodiment, substrate 18 may be a polyester film, such as Mylar®, thathas been precoated with a layer of indium tin oxide (ITO) to formelectrode 14. Preferably, the film has been precoated with a 90 to 500ohms per square layer of ITO, and most preferably with a 450±150 ohmsper square layer of ITO. Of course, materials other than ITO may be usedto form the electrodes of the apparatus of the present invention. AMylar® film with a precoated ITO electrode, known as Intrex, may bepurchased from Sierracin of Sylmar, California. Such an electrode-coatedfilm is very flexible.

As noted, latex entrapped NCAP liquid crystal is used in a preferredembodiment. Latex entrapped NCAP liquid crystal comprises the entrapmentof liquid crystal in a latex medium. The latex is a suspension ofparticles. The particles may be natural rubber or synthetic polymers orcopolymers. A latex medium is formed by drying a suspension of suchparticles. A further explanation of latex entrapped NCAP liquid crystaland methods of making the same are provided in U.S. patent applicationSer. No. 591,433, filed Mar. 20, 1984, in the name of Pearlman, entitledLATEX ENTRAPPED NCAP LIQUID CRYSTAL COMPOSITION, METHOD AND APPARATUS,assigned to the assignee of the present invention, and which disclosureis hereby incorporated by reference.

Briefly, latex entrapped NCAP liquid crystal may be formed by mixing asuspension of latex particles and liquid crystal material wherein theliquid crystal material has been previously emulsified in an aqueousphase. Alternatively, all components may be combined prior toemulsifying the liquid crystal material. The mixture may then be appliedto substrate 18 and electrode 14. As the mixture dries, it adheres tothe electrode-coated side of the polyester film. When dried, the latexparticles form a latex medium with particles of liquid crystal dispersedtherein.

A specific method for making latex entrapped NCAP liquid crystal maycomprise first emulsifying 36 grams of the liquid crystal ROTN701(manufactured by Hoffman La Roche of New York, N.Y.) in a solutioncontaining 14 grams of a 12% aqueous solution of PVA and 1 gram of thesurfactant TWEEN 20 (available through ICI Americas Incorporated ofWilmington, Del.). The liquid crystal is added continuously while thesolution is mixed with an impeller blade at 3500 RPM. When the particlesize of the liquid crystal is about 1-5 microns, 49 grams of NeorezR-967 (manufactured by Polyvinyl Chemical Industries, Wilmington,Mass.), containing 40% latex particles by weight, is added with slowmixing of less than 1000 RPM until the mixture is homogenous. Thismaterial may then be cast with a doctor blade or other suitable meansonto substrate 18 and electrode 14.

After the NCAP liquid crystal material has dried onto electrode 14 andsubstrate 18, substrate 12 and electrode 13 may be laminated onto thesurface of the latex entrapped NCAP liquid crystal material. Substrate12 may also be a flexible, Mylar® film precoated with a 90 to 500 ohmsper square, most preferably a 450±150 ohms per square, layer of ITO toform electrode 13.

In accordance with an aspect of the present invention, light, forexample that represented by a light beam 19 (see FIGS. 1 and 2),incident on the liquid crystal material will be scattered to yield awhite or bright appearance from a viewing area or side 30 when theliquid crystal is in a field-off or random alignment state, and a darkappearance when the liquid crystal material, or a selected portionthereof, is in a field-on or ordered alignment state. The presentinvention enhances the effective contrast between the characters orinformation displayed and the background.

It is noted that light incident on apparatus 10 will be refracted, dueto a mismatch in indices of refraction, as it passes through thedifferent materials that comprise apparatus 10. Apparatus 10 may beused, for example, in an air environment, represented by the referencenumeral 40. The air forms an interface 42 with the substrate 12 at thefront side or from the viewing direction 30.

As shown in FIG. 1, the liquid crystal material 20 is in a randomalignment when in the field-off state. Incident light beam 65 enterssubstrate 12 at the interface 42 and is refracted, (see light beam 65a)ultimately impinging as incident light beam 70a on the layer of liquidcrystal. The random or distorted liquid crystal material will scatterthe light incident thereon. There are several possibilities of how suchincident light beam 70a would tend to be scattered.

For example, one possibility is that the incident light beam 70a will bedirected according to the dotted line 70b through the layer of liquidcrystal material toward the non-viewing side 32 thereof. Light beam 70bmay impinge, as will be discussed below, on a reflective surface at thenon-viewing side to be reflected as light beam 70c back to the layer ofliquid crystal material where it will be treated as anotherindependently incident light beam thereto, just like the light beam 70afrom which it was derived. Therefore, such light beam 70c will undergoscattering, further enhancing the brightness of the background of thedisplay.

Another possibility is that the incident light beam 70a, or that derivedtherefrom, such as the light beam 70c, will be scattered toward theinterface 42 at an angle that is so close to normal at that interfacethat the light beam will pass through the interface 42 into the medium40 to be viewed by an observer or observing instrument. Light beam 70drepresents such a light beam emitted from the apparatus 10. It is thatlight, for example, the sum of such emitted light beams 70d, which exitsat the interface 42 that causes the liquid crystals to give theappearance of a white or bright background when viewed from the viewingside 30.

Referring to FIG. 2, the field-on or ordered alignment state andoperation of the liquid crystal apparatus are shown. Particularly, anelectric field E has been applied between electrode 13 and electrode 14.For instance, if electrode 14 is configured to form a figure-eightpattern, selected conductive segments may be energized to display thedesired numeral. The light beams 72 and 74, for instance, would betransmitted through the aligned and, thus, effectively transparent ornon-scattering liquid crystal material located between the energizedelectrodes.

Light beams 72 and 74 will be focused, as discussed below, by an opticalmeans on a target means. The sum of such focused light beams display theselected numeral, character or other information to an observer at theviewing location 30. Particularly, to an observer at viewing side 30,the area between the energized electrodes may appear very dark whereinthe light beams are focused onto a target means comprising a blackabsorber for absorbing at least substantially all of the light incidentthereon.

The liquid crystal material that is not located between the energizedelectrodes is still in the field-off state. Thus, the material stillscatters light incident thereon from both the viewing and non-viewingsides. Therefore, the numerals or other information displayed appear asvery dark characters against a very brilliant or white background.

One embodiment of the present invention is illustrated in FIG. 3. Thisembodiment includes a liquid crystal apparatus 10 as part of a laminateddisplay assembly comprising a target means 50 and a reflecting means 52.The target means and the reflecting means form a back plane of thedisplay. Light incident on apparatus 10 from the front or viewing side30 thereof is either scattered or transmitted therethrough. Thetransmitted light is focused onto the target means by the reflectingmeans. Whether such incident light is focused or defocused (scattered)depends on whether an electric field is applied to the liquid crystal orsome portion thereof.

The reflecting means may comprise an array of cylindrical mirrors 54having a radius of curvature R. Mirrors 54 present a concave surface tolight incident thereon. The mirrors may be formed by partial cylinders;for example, they may be formed from one-eighth to one-quartercylinders. The dimensions of the mirrors in the "x" or horizontaldirection is substantially equal to the dimension of the display in thatdirection. The number of mirrors in the array is dependent upon theheight or dimension of the display in the "y" or vertical direction.

The target means is disposed between the reflecting means and the liquidcrystal means. The target means may comprise a plurality of blackstripes 56 for absorbing substantially all of the light incidentthereon. Stripes 56 may be formed on an optically transparent substrate57. Alternatively, for a colored display, the target means couldcomprise colored stripes for abosrbing only one or more specifiedwavelengths of light.

Targets 56 may be located at a distance "d" of between 0.4 R and 0.5Rfrom mirrors 54 (See FIG. 4). Most preferably, targets 56 are locatedinwardly of the focal point of the mirrors. Optimally, in order toprevent the phenomenon of coma, they are located at a distance "d" of0.469R from the mirrors.

The targets' dimension in the "x" direction is substantially equal tothe dimension of the mirrors in that direction. As a result, the viewingangle of the display in the "x" direction or plane is approximately180°. For instance, if the display is located in a room, an observer atthe front or viewing side 30 of the display would be able to see theinformation displayed, ignoring for the moment the limitation on theviewing angle in the "y" direction, from a wide angle within the room.

The angle of view "A" of the display in the "y" direction or plane islimited. This angle of view is dependent upon the height "h" of thetarget (See FIG. 4). Particularly, the greater the height "h" the widerthe angle of view "A". Mathematically, the angle of view "A" isrepresented by the equation 2 arctan h/2f where "h" is the height of thetarget and "f" is the focal length of the mirrors of the optical system.As is known, f=R/2.

Therefore, an increase in the viewing angle "A" may be obtained byincreasing the height of the target. An increase in the viewing angleis, however, achieved at the expense of a loss of contrast between theinformation displayed and its background. That is, the taller the targetthe less brilliant is the display. A good trade off between viewingangle and contrast is obtained for a target height "h" of about 0.125R.This height provides a viewing angle "A" of approximately 20° (±10), andthe loss of brightness of the display is only about 20%. A viewing angle"A" of ±10° is suitable for most applications, for example, billboarddisplays which are viewed from relatively long distances and automobiledashboard displays which are viewed at relatively short distances.Generally speaking, if a display is to be viewed from a relatively shortdistance, the viewing angle "A" should be wider than a display which isto be viewed at a relatively long distance.

The liquid crystal apparatus 10 is preferably located at a distance Rfrom mirrors 54. As noted, light transmitted by apparatus 10 is focusedonto a target disposed between a mirror and the selected portion of theliquid crystal apparatus 10 to which a prescribed input, such as anelectric field, has been applied.

The ray trace of FIG. 4 illustrates that light, represented by lightbeams 58a, transmitted by the liquid crystal apparatus in the field-onstate impinges on the concave surface of mirror 54 disposed in back ofthe energized portion of the liquid crystal apparatus. This light isfocused, as illustrated by light beams 58b, onto target 56. Moreparticularly, within a prescribed viewing angle or viewing cone "A",light from an observer or observing instrument 90 from viewing side 30of the display is focused onto the target. Thus, if the target comprisesa black absorber, the information displayed by the energized portion ofthe liquid crystal will appear as a very dark character, numeral, etc.against a very white or brilliant background to an observer 90 withinthe prescribed viewing angle. The appearance of the display is furtherenhanced by the fact that some of the light impinging upon thereflecting means will be reflected back to the liquid crystal apparatusto undergo scattering, thereby further increasing the brightness of thedisplay.

The display assembly illustrated in FIG. 3 may be structured in an airenvironment. However, improved results are obtained, in the sense thatthe angle of view is increased, if the assembly, including the liquidcrystal means, the target means and the reflectors, are supported andcontained in a support medium 60 having an index of refraction greaterthan that of air. Thus, support medium 60 may be formed of suchmaterials as acrylic, polyvinyl alcohol, or polycarbonate.

The above assembly may form one of a plurality of modules which can bestacked in rows and columns to form a larger display. An illuminationsource on the viewing side of the display may also be provided toenhance the appearance of the display, that is, the contract between thecharacter or other information displayed and the background.

FIGS. 5A and 5B illustrate alternate embodiments of the presentinvention. These embodiments include a lens system 62, preferablycomprising convex lenses, disposed between liquid crystal apparatus 10and a target means 64. These embodiments also preferably include abacklighting scheme represented by light sources 28 and diffuser 29 (notshown in FIG. 5B).

As shown in FIG. 5A, the lens system 62 may comprise an array of spheres66 stacked on top of and adjacent to one another to form a plurality ofcolumns and rows of spheres. Alternatively and more preferably, as shownin FIG. 5B, lens system 62 comprises a plurality of cylindrical rods 75disposed adjacent to one another. The lens means (the rods or spheres)may be formed from such materials as acrylic, polyester, polystyrene,glass, polycarbonates, or various other optically transmissivematerials.

In the embodiment of FIG. 5A, the targets comprise a plurality of spotsor dots 68 located at the backside of each of the spherical lenses.Preferably, spots 68 are located at the focal point of the lenses, andare thus spaced from the back surface of the lenses for optimum results.In such an arrangement, the targets or spots 68 may be formed in thesupport medium means 60, or in a substantially optically transparentsubstrate located behind the lenses. An acceptable display is alsoobtained if the dots are formed on the back surfaces of the spheres. Asdiscussed heretofore, the targets may comprise black or coloredabsorbers.

In the embodiment of FIG. 5B, the targets may comprise a line or stripe77 extending along the back surface of each cylindrical rod 75.Optimally, stripes 77 are spaced from the back surface of the rods to belocated at the focal point thereof. The stripes, however, may be coatedon the back surface of the cylindrical rods. Stripes 77 may be black orcolored absorbers.

The angle of view or viewing cone of the displays of FIGS. 5A and 5B inthe "y" direction is limited and dependent upon the size of theirrespective targets. The angle of view in the "x" direction of theembodiment of FIG. 5B is approximately 180° as discussed with respect tothe embodiment of FIG. 3. The angle of view in the "x" direction of theembodiment of FIG. 5A is, however, limited by the size of the target.For a circular spot or target, the angle of view in the "x" direction isequal to the angle of view in the "y" direction.

The ray trace of the embodiment of FIG. 5B is shown in FIG. 6. Theheight "h₁ " of the respective stripes 77 determines the angle of view"B" of the display in the "y" direction. The greater the height "h₁ "the larger is the angle of view. However, as discussed previously, anincrease in the angle of view is achieved by a decrease in thebrightness of the display.

In the embodiment of FIG. 5B, for an angle of view of 20° (±10°), theheight "h₁ " of stripes 77 is approximately equal to one-sixth thediameter of cylindrical rods 75. In the embodiment of FIG. 5A, toachieve approximately the same angle of view, the angle of view in the"x" and "y" directions being equal for a circular target, the diameterof spots 68 may be approximately one-sixth the diameter of spheres 66.The embodiment of FIG. 5A is especially suitable for displays that areto be viewed by an observer at a relatively fixed position, forinstance, an automobile dashboard display. This embodiment is lesssuitable for displays which are to be viewed from widely-varyingpositions in the "x" direction, for example, a scoreboard display.

The liquid crystal means of either embodiment is preferably spaced fromthe lens system a distance approximately equal to twice the diameter ofthe spheres or cylindrical rods. Such positioning provides betteruniformity of illumination.

As noted, the embodiments of FIGS. 5A and 5B preferably include abacklighting scheme represented by light sources 28 at the back ofnon-viewing side 32 of the display (See FIG. 5A). The backlightingscheme may include a diffuser 29 to soften the light from illuminationsources 28. The backlighting scheme is utilized to overcome frontsurface glare, and to enhance the appearance of the display especiallywhen operated other than in bright sunlight.

The light provided by light sources 28 is scattered by the liquidcrystal of apparatus 10 in the field-off state to increase thebrightness of the background of the display.

If the liquid crystal is in the field-on state, the backlight isinvisible to an observer 90 within the prescribed viewing angle "B".Such an observer is only able to see the black image established by thelens system and the target means. Particularly, the target meansobscures the light from illumination sources 28 and the lens systemfocuses the parallel light rays, represented by rays 67a (See FIG. 6),originating from an observer within the prescribed viewing angle "B"onto to the target means as shown by light beams 67b. Therefore, to anobserver 90 within the viewing angle "B", the characters or otherinformation in back of the selected energized portion of the liquidcrystal will appear very dark against a very white background.

The embodiment illustrated in FIGS. 7 and 8 is an improved display thateliminates front surface glare. This embodiment utilizes the flexiblenature of the substrates between which the NCAP liquid crystal isdisposed to eliminate front surface glare. Liquid crystal apparatus notutilizing flexible substrates could not perform satisfactorily in thisembodiment.

The NCAP liquid crystal apparatus 10, which comprises a flexible film,is formed to present a concave surface to incident light, such as thatrepresented by light beam 19. Disposed immediately behind the NCAPliquid crystal apparatus is a reflector means 80 presenting a concave,reflecting surface to incident light. The reflector means may comprise apositive concave mirror having a radius of curvature R. The radius ofcurvature of the NCAP apparatus would also be R.

The reflector means 80 may be constructed by coating the surface of asubstrate 80a, such as one made from glass, metal or plastic, with athin layer of a reflecting metal 80b, such as aluminum or silver. Theelectrode 14 of NCAP apparatus 10 may be formed on substrate 18, andreflector means 80 suitably laminated to that substrate. Alternatively,substrate 18 may be eliminated, and electrode 14 formed on the surfaceof the reflector means by etching that surface to form the desiredelectrode pattern.

A target 82 is disposed in front of or on the viewing side 30 of theliquid crystal apparatus. The target may be located at a distance "d₂ "of between 0.4R and 0.5R from reflector 80. Preferably, the target islocated inwardly of the focal point of reflector 80 at a distance of0.469R from the reflector. In a preferred embodiment, the target isL-shaped comprising vertical and horizontal surfaces 82a and 82b,respectively. These surfaces may comprise black or colored absorbers.

The viewing angle in the "x" direction of the display is a function ofthe width "w₂ " of surfaces 82a and 82b. For a viewing angle of 90°, thewidth "w₂ " is preferably equal to the width of the display plus theradius of curvature R of reflector means 80. Particularly, surfaces 82aand 82b extend beyond the display by a distance R/2 at each side thereofsuch that the dimension "w₃ " is equal to R/2 (see FIG. 8).

The height "h₂ " of surface 82a and the length "l₂ " of surface 82b (SeeFIG. 8) determine viewing angle "C" in the "y" direction. For a viewingangle "C" of 20° (±10°), the height "h₂ " is approximately 0.0625R, andthe length "l₂ " of horizontal surface 82b is approximately 0.1R orgreater. The angle of view "C" is related to the height of the target bythe equation 2 arctan h₂ /2f where "f" is the focal length of reflectormeans 80.

The target 82 may be modified by replacing the horizontal and verticalabsorbing surfaces with a single vertical absorbing surface located atapproximately the focal point of the reflector. For a viewing angle inthe "y" or vertical direction of 20° (35 10°), the height of the singlevertical surface would be approximately 0.125R. The width of such avertical surface determines the angle of view in the "x" direction, asdiscussed with respect to surfaces 82a an 82b. The target may alsoinclude a hood for shielding the light-absorbing surfaces of the targetfrom direct sunlight. For instance, a hood 86 may be utilized to shieldsurfaces 82a and 82b.

As shown by FIG. 9, light incident on the display, represented by lightbeams 85a, within a controlled viewing angle "C" impinges on thereflecting surface of reflector 80 where it is focused onto thehorizontal and vertical surfaces of target 82, as shown by light beams85b. The light that is focused on the target, where the target is ablack absorber, presents an extremely dark image or display to anobserver 90 within the prescribed viewing angle.

The glare on the front surface of the display of this embodiment isspecular. This embodiment eliminates that glare by focusing it onto thetarget, or at least the glare at the energized portion of the NCAPliquid crystal. The glare at the de-energized portion of the liquidcrystal is not a problem.

The glare-reduction display of FIG. 7 as well as the other embodimentsdiscussed are adaptable to such displays as outdoor billboards, indoordisplay signs, automobile dashboard displays, window mounted displays,gas price signs, time and temperature signs, and scoreboards bothportable and fixed.

Ideally, if the display of information is to be observed from above, thetarget should be located at bottom of the display. Conversely, if thedisplay of information is to be observed from below, the target shouldbe at the top of the display. The embodiment depicted in FIG. 7 may beutilized as billboard which would be observed from below the display. Inthis embodiment, the target is located at the bottom of the display toprevent shadows from being cast onto the display, which is contary tothe preferred arrangement of the target and the display.

The display of FIG. 7 may use cylindrical, hyperbolic, parabolic, orelliptical cross-sections to reduce target size or improve thedimensions of the display apparatus. A support medium means 60 may beused to support and contain the reflector and liquid crystal means.

As noted, present invention is not limited to use with liquid crystalmaterials. The embodiment of FIG. 7, for instance, may be used to reduceor eliminate specular glare from almost any type of display where suchglare is a problem, for example, a white-faced chalkboard or aglossyfaced billboard. In this context, this embodiment will comprise alight absorbing target and a concave reflector means for focusingspecular reflection onto the target.

The present invention may also be used in alternate embodiment whereinbright characters are displayed on a relatively dark background. In suchan embodiment, the liquid crystal material located in the displaysegments used to form the character or information displayed would be ina field-off state such that light is scattered to create charactershaving a bright appearance. The liquid crystal material in the displaysegments surrounding the character segments would be in a field-on statesuch that light is appropriately focused onto suitable targets to createa relatively dark background.

Although certain specific embodiments of the invention have beendescribed herein in detail, the invention is not to be limited only tosuch embodiments, but rather only by the appended claims.

What is claimed is:
 1. A display comprising means having two states, onestate for scattering incident light and a second state for transmittingincident light as a response to a prescribed input independent of theincident light, and focusing means for directing unscattered lighttransmitted through said scattering or transmitting means onto a lightabsorbing target means external to and on a non-viewing side of saidscattering or transmitting means for enhancing the contrast of thedisplay.
 2. The display of claim 1 wherein said scattering ortransmitting means comprises a liquid crystal means.
 3. The display ofclaim 2 wherein said liquid crystal means comprises at least one layerof nematic curvilinearly aligned phases liquid crystal material.
 4. Thedisplay of claim 1 wherein said optical means has a focal point and saidtarget means is located at approximately said focal point.
 5. The liquidcrystal apparatus of claim 4 wherein said target means comprises a blackabsorber for absorbing substantially all of the light incident thereonor a colored absorber for absorbing only one or more specifiedwavelengths of light.
 6. A display, comprising:means selectivelyoperable for affecting light incident thereon and having two states, onestate for scattering light and a second state for transmitting light inresponse to a prescribed input independent of the incident light; atarget means located on a non-viewing side of said selectively operablemeans for absorbing light incident thereon; and a lens means disposedbetween said selectively operable means and said target means fordirecting light transmitted through said selectively operable means ontosaid target means to enhance the contrast of the display.
 7. The displayof claim 6 wherein said selectively operable means comprises a liquidcrystal means.
 8. The display of claim 7 wherein said liquid crystalmeans comprises at least one layer of nematic curvilinearly alignedphases liquid crystal material.
 9. The display of claims 6, 7 or 8further including an illumination source on the non-viewing side of thedisplay for directing light toward said lens means.
 10. The display ofclaim 9 wherein said lens means comprises a plurality of cylindricalrods disposed adjacent to one another.
 11. The display of claim 10wherein said target means comprises a stripe extending substantiallyalong the length of each of said cylindrical rods.
 12. The display ofclaim 11 wherein said target means is positioned between the backsurfaceof said lens means and the focal point thereof.
 13. The display of claim12 wherein said strip comprises a black absorber for absorbing at leastsubstantially all of the light incident thereon or a colored absorberfor absorbing only one or more specified wavelengths of light.
 14. Thedisplay of claim 12 wherein the height of said stripes is approximatelyequal to one sixth the diameter of said cylindrical rods.
 15. Thedisplay of claim 12 wherein said selectively operable means is spacedfrom said cylindrical rods a distance approximately equal to twice thediameter thereof.
 16. The display of claims 6, 7 or 8 wherein said lensmeans comprises a plurality of spheres disposed adjacent to one another.17. The display of claim 16 wherein said target means comprises a dotlocated at the backside of each of said spheres.
 18. The display ofclaim 17 wherein said dot is positioned between the backside of saidspheres and the focal point thereof.
 19. The display of claim 18 whereinthe diameter of said spots is approximately equal to one-sixth thediameter of said spheres.
 20. The display of claim 18 wherein said dotcomprises a black absorber for absorbing at least substantially all ofthe light incident thereon or a colored absorber for absorbing only oneor more specified wavelengths of light.
 21. The display of claim 18wherein said selectively operable means is spaced from said spheres adistance approximately equal to twice the diameter thereof.
 22. A methodfor contrast enhancement, comprising:scattering or transmitting incidentlight by means of an electro-optical device as a response to a givenelectrical input independent of incident light, said electro-opticaldevice having two states, a first state for scattering light and asecond state for transmitting light; and focusing unscattered lighttransmitted through said electro-optical device onto a light absorbingtarget means external to and on a non-viewing side of saidelectro-optical device for enhancing contrast.
 23. A display,comprising:liquid crystal means operable for affecting light incidentthereon and having two states, one state for scattering light and asecond state for transmitting light in response to a prescribed inputindependent of the incident light; a target means located on anon-viewing side of said liquid crystal means for absorbing lightincident thereon; and a plurality of cylindrical lenses disposed betweensaid liquid crystal means and said target means for directing lighttransmitted through said liquid crystal means onto said target means toenhance the contrast of the display.
 24. The display of claim 23 whereinsaid lenses comprise cylindrical rods.